1. Technical Field
The present disclosure relates to a stencil mask and a manufacturing method thereof, which is utilized for forming a pattern according to lithography technology using a charged particle beam such as an electron beam, and more particularly, to a stencil mask and a manufacturing method thereof using a thin film membrane supported by a strut.
2. Discussion of Related Art
As the design rule of semiconductor integrated circuit devices has decreased, lithography technologies utilizing a particle beam such as an X ray, an electron beam, and an ion beam have been developed to enhance resolution of optical instruments. Among the various types of lithography, electron beam projection lithography has an advantage of forming a fine pattern at a scale of 1 μm or less. Thus, various systems and pattern forming methods using this lithography technology have been proposed. One example is disclosed in U.S. Pat. No. 5,831,272.
Electron beam proximity projection lithography (EPL) and low energy electron beam proximity projection lithography (LEEPL) project a pattern onto a resist by permeation of the electron beam through a fine aperture formed on a stencil mask.
FIG. 1 is a perspective view of a partial composition of a conventional stencil mask 10 used in EPL or LEEPL. Referring to FIG. 1, the conventional stencil mask has a plurality of membrane areas 12 respectively patterned by a fine aperture (not shown) and divided by border areas, which are not patterned. The border areas include support struts 14 which are formed of rows and columns, which intersect perpendicularly and reinforce mechanical durability of the stencil mask 10.
FIG. 2 is a cross-section illustrating a portion of the stencil mask 10 of FIG. 1. Referring to FIG. 2, apertures 12a corresponding to fine patterns are formed in the membrane areas 12. If electron beams 20 are projected onto the stencil mask 10, the fine pattern is projected onto a resist layer (not shown) coated on a wafer after the electron beams permeate the apertures 12a. 
The apertures 12a are formed by etching the membrane areas 12. In a case where the fine pattern is used for manufacturing a next generation highly integrated device, for example, when the fine pattern at a scale of 0.1 μm or less is required, the apertures 12a must be formed to have a line width on a scale of 10's of nm. In this case, the ratio of the thickness of the membrane areas 12 to the diameter of the apertures 12a, i.e. the aspect ratio of the apertures 12a, should be small enough to accurately form a desired profile of the apertures 12a during etching of the membrane areas 12. Specifically, the aspect ratio of the apertures 12a must be reasonably maintained and the thickness of the membrane areas 12 should be as thin as possible, for instance, at about 1 μm or less and preferably 500 nm or less.
However, thin membrane areas 12 bend easily, resulting in a tensile stress inside the membrane areas 12. The tensile stress causes the membrane areas 12 to transform or distort, and thus image placement error occurs since the pattern projected through the membrane areas 12 becomes displaced.
Various mask structures have been suggested to solve the above problems, such as U.S. Pat. No. 6,261,726 B1 and Japanese Patent Publication No. hei 15(2003)-59819. However, these masks, which include a structure to support the membrane, mostly use the conventional strut structure described above and thus have limitations in preventing image placement error due to the transformation or distortion of the membrane. Accordingly, there is a need for a stencil mask in which occurrence of image placement error due to transformation or distortion induced by internal stress inside membrane areas is substantially diminished without limiting size or aspect ratio of the membrane areas.